Motor fuel composition



United States Patent Ofiice 3,2275% Patented Jan. 4, 1956 3,227,531 MSTQR FUEL CGMPQSI'I'EQN Louis N. Qalvino, Plainfield, and l ehn B. Turner, North Plaini'ield, Ni, assignors to Ease Research and Engineerlng Company, a corporation of Belawtu'e No Drawing. Filed July 18, 1951, Ser. No. 124,816 4 (Ilaims. (Cl. 44-58) The present invention relates to improved motor fuels and a method of operating an engine which tends to promote engine cleanliness and particularly to gasoline compositions for internal combustion engines containing improved solvent oils of enhanced stability. More particularly, the instant invention concerns improved hydrocarbon solvent oils having incorporated therein stabilizing amounts of a polymeric additive.

Solvent oils, both synthetic and hydrocarbonaceous, are commonly employed in minor amounts as motor and aviation fuel additives to serve as a general purpose, upper cylinder lubricant to reduce vmve stem and piston ring sticking and to decrease manifold and intake port deposits. One of the primary functions of these motor fuel solvent oils is to aid by selective solvent action in the removal of gum, resins, varnishes and sludge. However, oxygenated gums and resins are not readily removed by these solvent oils, and it would be highly desirable to employ as a solvent oil, or as an adjuvant to solvent oils, a stable composition that has hi h specificity for gums and varnishes. In the past, various oxygenated solvents have been added to gasoline for this purpose, but these materials have not been wholly eifective, either because of too high vapor pressure at motor operating conditions, or because excessive quantities were required. Thus, it has been suggested that high boiling esters such as amyl stearate be employed as a solvent oil. Such esters, however, have not given satisfacion and their solvent powers are inadequate.

The need for a highly active stable solvent oil type additive has been long recognized. A tendency to cause manifold deposit and intake port deposit buildup represents a serious fuel deficiency, particularly when the fuel is used in low temperature service with considerable engine idling time. Catalytically cracked gasolines which have comparatively high octane numbers and are thus widely used are unstable and require the use of an antioxidant. Both these unstable fuels and antioxidant residues contribute to manifold deposits. Use of a solvent oil type additive represents a desirable method of minimizing these deposits.

It has now been discovered that superior solvent oils may be prepared by incorporating minor amounts of a high molecular weight, ashless, oil soluble polymeric additive in the solvent oil. In particular, it has been found that those high molecular weight, ashless, oil soluble polymers which function as multifunctional viscosity index improvers in heavy lubricating oils are surprisingly effective in promoting overall intake and fuel system cleanliness and in enhancing the oxidation stability of solvent oils. More particularly, it has been found that the addition of small quantities to a light mineral distillate solvent oil or upper cylinder lubricant of a terpolymer of maleic anhydride, vinyl ester and alkyl fumarate enhances the stability characteristics of the solvent oil and the motor fuel in which the solvent oil is employed.

This is a significant and surprising discovery, since the use of high molecular weight polymeric materials in light solvent oils and volatile fuels has been avoided in the past in the belief that such additives would increase the amount of combustion and manifold deposits and promote the formation of additional sludge and deposits. Additionally, it was believed that polymeric type additives would fail to function as detergents or dispersants in a volatile fuel like gasoline, especially after being combusted at high temperatures in a combustion chamber.

The advantages of the present invention allow an improved solvent oil to be added to gasoline fuels, and the polymeric additive to have multifunctional properties in stabilizing the solvent oil against excessive oxidation, reducing manifold or intake system deposits, and additionally promoting overall fuel system and carburetor cleanliness and also throughout those engine areas not having direct liquid contact with the heavy crankcase lube oil. The present invention also allows for reduced quantities of the polymeric additives to be employed in a more elfective direct manner in reducing sludge and sediment. Previous to this discovery, polymeric additives in general were restricted to heavy lubricating oils to aid in suspending the sludge derived from the original volatile fuel composition, such as the unstable cracked fuel components, the additive in the fuel such as the antioxidant, and the combustion and blow-by products of the fuel. The applicants have thus discovered a direct method of both promoting fuel system, intake system and engine cleanliness and enhancing solvent oil stability.

The solvent oils in which the polymeric additive of the instant invention may be beneficially employed comprise synthetic and mineral solvent oils having an SUS viscosity of between about 50 and 2009 at F., e.g. 56 to 500, and those having an SUS viscosity of about 30 to at 210 F, and a Conradson carbon content of less than 1 wt. percent. The synthetic solvent oils include those oxygenated nonvolatile compounds such as fatty acid esters like amyl stearate; ester type oxidates derived from deoiled macrocrystalline wax as set forth in U.S. Patent 2,965,458; polyoxyalkylene compounds as in US. Patents 2,897,525 and 2,807,526; and other organic, oil soluble, oxygenated, high solvency types of nonvolatile compounds and mixtures thereof.

These synthetic solvent oils also include those liquid synthesis products derived from the 0x0 processes as set forth in US. Patent 2,955,928 and those Oxo bottoms acylated by treatment with ketene or acetic anhydride and the like as set forth in US. application Serial No. 15,527, filed March 17, 1960, now US. Patent No. 3,054,666. Those high molecular weight esters, others, alcohols, aldehydes, preferably saturated having more than an average of 16 carbon atoms per molecule and boiling above about 259 F. are the preferred synthetic solvent oils.

The petroleum solvent oils may be a naphthene base distillate, a paraffin base distillate or mixtures thereof. These solvent oils are completely obtained by vacuum distillation of the base oil at from 20 to 40 mm. pressure and subsequent acid treatment, caustic washing or hydrofining or any combination of the distillate. These mineral oils may also comprise those silica gel extracted bright stocks obtained by the select silica gel treatment of a deasphalted, solvent extracted, dewaxed virgin residual or bright stock as described in US. Patent 2,904,493, for example, a bright stock having an SUS viscosity of 1858 at 100 F. and 132 at 210 F.

The preferred solvent oils are those light liquid hydrocarbon mineral distillate oils having an SUS viscosity at 100 F. of between 50 and 300, e.g. 70 to 90. Suitable solvent oils include those oils having a 50% distillation point above 350 F. at 10 mm. Hg pressure, having a Saybolt viscosity at 100 F. not above 450 seconds, and having an API gravity of about 18 to 28. A typical solvent oil, for example, has the following inspection:

50% distillation point @10 mm. Hg, F. 413 Saybolt viscosity 100 F., SUS 75.3 API gravity 26.6

Mineral solvent oils are usually light solvent lubricating oils or low viscosity naphthenic distillates, but may be petroleum, animal or vegetable sources or mixtures thereof. In general, mineral solvent oils have aniline points of 160 F. to 170 F. and API gravities of 25 to 28. Conventional solvent oils are described in US. Patent 2,066,234 issued to Sloane and Wasson on December 29, 1936, and U.S. Patents 2,579,692, 2,646,348, and 2,654,- 697 and others recited which are inconporated by reference.

The solvent oils of the invention may be mineral or synthetic solvent oils as described or combinations thereof such as from 40 to 80% mineral oil or even 50 to 90% mineral oil, and may contain other additives such as detergents; halogenated aromatic compounds; acid tars; oiliness additives; metal deactivators such as N,N'-disalicylidene-l,Z-diaminopropane; preignition additives such as alkyl-aryl phosphates like tricresyl phosphate, tri-B-chloroethyl phosphate, amine phosphates, and the like; antioxidants such as 2,6-ditertiary-butyl-4-methyl phenol, N,N-di-secondary-butyl-para-phenylene diamine, N-butyl para amino phenol, and the like; dyes; antirust additives such as amines and phosphates and the like; anti-icing agents such as hexylene glycol, isopropanol; antiknocks; and the like.

The polymeric additives of this invention are multifunctional Vl. improper additive polymers such as those high molecular weight, ashless, oil soluble polymers obtained by copolymerizing maleic anhydride with an aliphatic ester of an a,,3-L1IISE1IUI81ICC1 dicarboxylic acid and a copolymerizable C to C alkylene ester of a C to C monocarboxylic acid. The preferred embodiment of this polymer includes the terpolyrner obtained by copolymerizing maleic anhydride, vinyl acetate, and C to C alkyl fumarate. The preferred polymeric additive agents are those terpolymers obtained by copolymerizing maleic anhydride, a vinyl ester of a short chain fatty acid, and a long straight chain C to C fatty alcohol ester of a butenedioic acid.

It is preferred that the esters of diand monocarboxylic acids used to form the coplymers of the present invention are so chosen that a mixture of relatively long and short aliphatic side chains is disposed along the polymer chain. The relatively long side chains may be provided by C to C aliphatic saturated or unsaturated, substituted or unsubstituted ester of C to C a,fi-t1nsaturated dicarboxylic acids, e.g. esters derived from C to C fatty alcohols, preferably alkyl alcohols. Straight .chain a1- cohols, branched chain alcohols, or a mixture of the two can be used. The preferred acids are 0a,,B-UI1S2ttUIflt0d conjugated dicarboxylic acids, such as butenedioic acid like fumaric acid although maleic or itaconic acid may be used. Suitable esters include monoand di-C OX0 furnarate, tallow fumarate, lauryl maleate, stearyl fumarate, C Oxo fumarate, and cetyl itaconate, and the like. The relatively short side chains are preferably provided by using C to C alkylene esters or ethers of C to C carboxylic acids, preferably vinyl or allyl esters such as allyl and vinyl esters of short chain C to C fatty acids like vinyl acetate and allyl acetate. Minor amounts, e.g. 1 to molar proportions of other ethyl- I A l B l C l D Maleic anhydride, percent 1-6 1-15 10-12 1-5 Alkyl ester of unsaturated dicarbozrylic acid, percent 20-50 25-50 -45 20-30 Alkylene ester of C1 to Ca monocarboxylic acid, percent -80 40-70 -55 -30 The molar proportions of column A are especially preferred and those of column D are most preferred.

The weight average molecular weights of the V.I. multifunctional additives may vary between 100,000 and 2,000,000 or more, e.g. 3,000,000, as determined by standard light scattering method, but preferably range between 500,000 and 2,000,000. Since the average molecular weight may vary depending on the length and character of the side chains, that is, the butenedioic acid esters employed, a more effective method of designating the polymer is by the degree of polymerization which clearly defines the main polymer chain length.

The degree of polymerization is defined as the number of carbon atoms in the main polymer chain divided by two. The multifunctional V.I. polymers of this invention have a degree of polymerization between about 500 and about 8,000 or more, such as 10,000, but preferably between 1500 and 5000.

The copolymers of the present invention may be prepared by any well known process, such as low temperature Friedel-Crafts polymerization, ionic or radiation polymerization processes. Free radical producing catalysts, e.g. peroxide type catalysts are particularly useful, such as benzoyl, acetyl, steroyl or urea peroxide or azo catalysts such as a,a-azo-bis isobutyronitrile may be employed.

If a free radical catalyst which decomposes at a temperature above C. is used to copolymerize the monomers, an improved copolymeric product is obtained compared with a similar product obtained using a free radical catalyst decomposing below 70 C., such as benzoyl peroxide. The preferred peroxide catalyst used in this improved process is organic alkyl and aryl peroxides such as alkyl perbenzoates and tertiary butyl perbenzoate. Other catalysts which may be used are tertbutyl hydroperoxide, 2,2-bis(tert-butyl-peroxy butane), di-tertiarybutyl peroxide, di-ctunyl peroxide.

Another Way of defining this improved process is that the copolymeric reaction is carried out at a temperature between 70 and 200 C., using a peroxide catalyst which does not decompose below 70 C.

The catalyst may be used in the form of an oil solution or slurry, and the reaction is preferably carried out under an inert gas, e.g. nitrogen, the reactants being agitated, either by stirring or bubbling the inert gas through the mixture. The reaction is carried out for a period of time sufiicient to copolymerize the reactants, but not for a time long enough to form an insoluble gel. A preferred criterion is to continue the reaction until the mixture reaches a viscosity of about 400 stokes at the reaction temperature, and then dilute the reaction mixture: with an oil, preferably a solvent oil of the type described, the copolymer being stripped under vacuum. The solvent oil or heavy mineral oil concentrate of the stripped polymer may then be incorporated in hydrocarbon motor fuels. The catalyst may be used in minor amounts such as from 0.001 to 5.0 wt. percent, e.g. 0.1 to 2 wt. percent. These high molecular weight polymers are further described in British Patent 807,737, which is hereby incorporated by reference.

The polymeric additives of this invention are incorporated in minor amounts betwen 0.1 and 20% by weight in the solvent oil or preferably between 0.5 and 15% by weight, for example, between 2 and 8 wt. percent. The improved solvent oil concentration may vary dependent upon the characteristics of the gasoline, the engine, and the type of driving conditions under which used, but is generally snihcient to reduce or control intake system deposits to an acceptable level. Solvent oils are commonly employed at a concentration of between 0.05 and 3.0 wt. percent and especially between 0.1 and 1.0 wt. percent based on the gasoline blend. The concentration level of the polymeric additive based on the motor fuel ranges between 0.001 and 0.5 wt. percent, and preferred is 0.005 to 0.2 wt. percent.

In carrying out the invention, a small amount of the improved polymeric containing solvent oil is either added directly to the motor or aviation gasoline itself or is injected into the intake system or manifold in any desired manner in order to contact the deposits and gum on the surface. The improved solvent oil of the present invention is also of beneficial use for fiuxing gummy deposits and the like from the fuel systems of diesel engines, oil burner installations, iet engines, turbines, and other deposit laden surfaces and, thus, may also be incorporated in diesel fuels, jet fuels, heating oils, and other hydrocarbon oils and fuels. It is, of course, recognized that the polymeric additive may be separately incorporated in the gasoline or in an oil concentrate containing other additives.

The motor fuels in which the polymeric additives are employed in order to reduce the formation of deposits, sludge and varnish are conventional petroleum distillate fuels boiling in the gasoline boiling point range employed in internal combustion, preferably spark ignition, engines. They are supplied in a number of different grades depending upon the type of service for which they are intended. The copolymers may be employed in all of these grades but are particularly useful in motor and aviation gasolines. Motor gasolines as referred to in connection with the present invention are defined by ASTM Specification D-439-58T in Types A, B and C. They are composed of a mixture of various types of hydrocarbons including aromatics, olefins, parafiins, isoparaffins, naphthenes and, occasionally, diolefins. Those motor fuels containing at least 10% by weight of thermally or catalytically high aromatic components may be especially benefited from the instant invention. polymeric additives of the instant invention may be added are those gasolines having an octane number range of 83 to 105 or higher, such as a clear octane number of over 90, for example, over 95 or 100, and comprising over 20% by volume of aromatic hydrocarbons and less than 30% by volume of olethnic hydrocarbons. They are derived from petroleum crude oil by refining processes such as fractional distillation, catalytic cracking, hydroforming, alkylation, isomerization, polymerization and solvent extraction. Motor gasolines normally have boiling ranges between about 70 F. and about 450 F, while aviation gasolines have narrower boiling ranges of between 100 and 330 F. T e vapor pressures of gasoline as determined by ASTM Method 13-86 vary between about 7 and about 15 psi at 100 F. The copolymers may also be employed in aviation gasoline, which have properties similar to those of motor gasolines but normally have somewhat higher octane numbers and narrower boiling ranges. The properties of aviation gasolines are set forth in US. Military Specification MIL-F4572 and ASTM Specification D91057T.

The copolymeric additives employed in accordance with the invention may be used in gasolines with other additive agents conventionally used in such fuels. It is common practice to employ from about 0.5 to about Suitable gasolines to which the 7.0 cc./ gal. of alkyl lead antiknock agents, such as tetraethyl lead, tetramethyl lead, dimethyl diethyl lead or a similar alkyl lead antiknock agent or olefinic lead antiknock agents such as tetravinyl lead, triethyl vinyl lead, and the like, or a combination thereof, in both motor gasolines and in aviation gasolines, e.g. 1.0 to 3.0 cc. of tetraethyl lead-tetramethyl lead combination. Antiknock agents may also include other organornetallic additives containing lead, iron, nickel, lithium, manganese and the like. Other additives such as those conventionally employed in gasolines may be used such as corrosion inhibitors, antioxidants, antistatic agents, lead octane appreciators-likht t-butyl acetate, auxiliary scavengers like tri-fl-chloroethyl phosphate, dyes, anti'icing agents like isopropanol, hexylene glycol and the like.

Catalytically and thermally cracked and reformed gasolines contm'ning a high aromatic content, whether leaded or unleaded, are particularly prone to yield excessive manifold deposits and are improved by addition of the applicants solvent oil composition.

Lead antiknock agents are usually employed in conjunction with halogenated hydrocarbon scavenger agents boiling in the range between and 250 F., such as ethylene bromide, ethylene chloride, and the like in concentrations of from 0.5 to 3.0 theories, with preferred concentration levels of from 0.8 to 1.5 theories of ethylene bromide used alone or 0.8 to 1.5 of ethylene dichloride and 0.3 to 0.8 of ethylene dibromide when a mixed scavenger is used.

The preparation of the high molecular weight polymers may be illustrated by the following examples.

EXAMPLE 1 The following monomer mixture is prepared:

Percent by wt.

Lauryl furnarate 75.2. Lauryl alcohol (reaction modifier) 2 Vinyl acetate 18.8 Maleic anhydride 4 The monomer mixture is then divided into two parts, part A being copolymerized at C. using 1 Wt. percent benzoyl peroxide and part B being copolymerized at C. using 0.4 wt. percent tertiary butyl perbenzoate. Copolymerization is continued in both instances until a reaction mixture having a viscosity of 400 stokes at the reaction temperature, and the copolymeric products diluted with an SAE 10 type mineral oil or a solvent oil. The solution is then stripped under a reduced pressure of 5 mm. Hg at C. until the solution contained 50% of the active polymer. The benzoyl peroxide polymer is designated as polymer A with the t-butyl perbenzoate designated as polymer B, each polymer having a chain length of about 3,000 to 10,000 carbon atoms.

EXAMPLE 2 The procedure of Example 1 is repeated exactly except that the materials polymerized are as follows:

Mole percent Di-C Oxo fumarate 17.8 Di-tallow fumarate 7.4 Vinyl acetate 71.8

Maleic anhydride 3.0

are prepared by reacting an olefin prepared by the reaction of butylene and propylene with carbon monoxide and oxygen to form a mixture of aldehydes which were hydrogenated. The di-C Oxo fumarate and di-tallow fumarates are mixed. The resulting mixture has an average molecular weight of about 420. Two wt. percent of benzoyl peroxide based on the total weight of the polymerizable materials is used as a catalyst. Two wt. percent of lauryl alcohol based on the total weight of the polymerizable materials is used as a moderator. The polymer was designated as polymer C and has a chain length of 3,000 to 10,000 carbon atoms.

EXAMPLE 3 The procedure of Example 2 is repeated exactly except that the materials polymerized are as follows:

Mole percent Di-C Oxo furnarate 14.6 Di-C Oxo fumarate 6.5 Di-tallow fumarate 4.0 Vinyl acetate 71.9 Maleic anhydride 2.9

The di-C Oxo fumarate is prepared by esterifying fumaric acid with a C Oxo alcohol. The C Oxo alcohols are prepared by the x0 process by reacting propylene tetramer with carbon monoxide and hydrogen to form a branched C aldehyde which is hydrogenated to form the C alcohol. The three fumarates are mixed to obtain a fumarate mixture having an average molecular weight of about 420. This polymer is designated polymer D.

EXAMPLE 4 The Sligh test is an accelerated oxidation test which measures the resistance of an oil to oxidation and the formation of sludge. A sample of the oil is placed in a specially constructed vessel which is charged with oxygen. The vessel is then heated in a bath for a specified time and at a specified temperature. At the end the oil is diluted with a light naphtha, filtered and the weight of precipitate reported as the Sligh number in milligrams of precipitate. The eifect upon the Sligh number of various gasoline solvent mineral oils with and without the polymeric additives is shown in the following Table I.

Table I OXIDATION STABILITY OF SOLVENT OILS CONTAIN- ING POLYMERIC ADDITIVES Sligh No. Solvent oil Y 1 14.3 Solvent oil Y plus 6 wt. percent polymer D 1.0 Solvent oil X 2 84.1 Solvent oil X plus 6 wt. percent polymer D 17.8

oSolvent oil T was a coastal distillate of about 80 SUS at 0 F 1 2 Solvent oil X was a methylethyl ketone dewaxed San Joaquin light distillate of about 79 SUS at 100 13.

These data clearly demonstrate the remarkable improvement in oxidation stability occasioned by the addition of a maleic anhydride, vinyl acetate, alkyl fumarate polymeric additive to mineral hydrocarbon solvent oils. Thus, the addition of only 6 wt. percent of the polymeric additive significantly reduced the amount of oxidation precipitate formed from the solvent oil indicating that the solvent oil with the additive had superior oxidation stability and would contribute to increased intake system and carburetor cleanliness when incorporated in motor fuels.

EXAMPLE To further confirm the superior results and relationship of the Sligh test and the ability of the improved solvent oil composition to reduce intake manifold deposits, additional tests were performed in a Lauson engine. In these tests, the Lauson engine was operated on an experimental gasoline blend similar to a commercial premium grade motor gasoline, then with the same gasoline containing 0.5 vol. percent of a mineral solvent oil, and finally using a sample of the same gasoline with the same mineral solvent oil containing a small amount of the polymeric additive. After each test, the manifold was washed first with heptane and then with acetone. The solvent was evaporated from the washing and the heptane insoluble acetone soluble deposits weighed and reported in milligrams of deposits per pound of fuel. The solvent oil and polymeric additive were the same as described in Table I. The gasoline used was an experimental premium grade gasoline.

Table II EFFECT OF IMPROVED SOLVENT OIL IN A LAUSON ENGINE MANIFOLD TEST Acetone soluble manifold deposits mgJlb. of gasoline Test Gasoline alone 2.0 Gasoline plus 0.5 wt. percent solvent oil Y 1. 1 Gasoline plus 0.5 wt. percent solvent oil Y and 0.015 wt. percent polymer D 0. 8

From these data, it is apparent that this improvement in oxidation stability as measured by the Sligh test is further reflected in actual Lauson engine tests. The above tests demonstrate that the improved solvent oil compositions effectively reduce manifold deposits to a very low level, and that the improved solvent oil composition is markedly superior to conventional mineral oils alone.

EXAMPLE 6 An untreated paraffinic base distillate of about 79 SUS/ F. from Venezuelan crude is greatly improved in oxidation stability by the addition of about 4 wt. percent of polymer A.

EXAMPLE 7 A gasoline solvent oil of enhanced stability characteristics is achieved by the addition of about 8 wt. percent of polymer C to a white oil obtained by exhaustive refining of a naphthene base distillate oil by H SO treating and having a viscosity of about 100 SUS at 100 F.

EXAMPLE 8 An improved solvent oil composition characterized by a relatively low tendency to form intake manifold deposits when added at a concentration level of about 0.5 vol. percent to a premium gasoline having a 50% ASTM distillation point of less than 210 F. and an ASTM gum level of more than 5 mg./ 100 cc. is obtained by the addition of about 3 wt. percent of polymer D and about 1.0 wt. percent of a monobutoxy poly-1,2-oxy propylene glycol and having a viscosity of about 300 SUS at 100 F.

EXAMPLE 9 A superior solvent oil having markedly improved oxidation stability is obtained by adding between 2 to 6 wt. percent of polymer D to a silica gel extracted, deasphalted, solvent extracted bright stock solvent oil having less than 5% aromatic content and a pour point less than +30 F.

9 EXAMPLE 11 An aviation gasoline with an initial boiling point of about 105 F., a mid boiling point of 210 F., and a final boiling point of about 315 F. is blended with about 4 cc. of tetraethyl lead per gallon, 1 theory of ethylene dibromide and 0.5 vol. percent of a highly refined acid treated and neutralized naphthenic base distillate having a SUS viscosity of about 100 at 100 F. and about 0.01 wt. percent of an ashless oil soluble polymer B. This fuel when used to operate a Continental aviation engine with direct injection contributes to improved engine intake and injection system cleanliness.

EXAMPLE 12 A highly aromatic motor gasoline containing 60% by volume of a catalytically hydroformed naphtha, a 425 F. ASTM distillation end point, a Reid vapor pressure of about 9 lbs. per square inch and a clear octane number of about 95 is upgraded in manifold and fuel system cleanliness characteristics by the addition of about 0.75 volume percent of a light solvent dewaxed hydrocarbon mineral paraffinic base solvent oil distillate and about 0.008 wt. percent of polymer D.

In summary, the applicants have discovered an improved solvent oil composition having enhanced stability, and which operates to elfectively reduce intake system deposits for a far greater degree than conventional solvent oils.

What is claimed is:

1. An improved motor gasoline characterized by a reduced tendency to form objectionable engine deposits, said gasoline containing solvent oil having viscosity of between 50 and 2000 SUS at 100 F. in a minor amount sufiicient to improve upper cylinder lubrication and a very small amount of a polymeric additive sufficient to impart oxidation stability to said solvent oil and to promote engine cleanliness, which polymer is obtained by copolymerizing from 1 to 6 molar percent of maleic anhydride with from 20 to molar percent of a C to C fatty alcohol ester of an 1:1,[3-11I1S8tl1121'tfid C to C dicarboxylic acid and with from 40 to 80 molar percent of a copolymerizable alkenyl C to C ester of an aliphatic monocarboxylic acid to give a polymer having a molecular Weight of from 100,000 to 3,000,000.

2. A composition as defined in claim 1 wherein said solvent oil is a hydrocarbon solvent oil and said minor amount is from 0.05 and 3.0 wt. percent.

3. A composition as defined in claim 1 wherein said very small amount is between 0.005 and 0.5 wt. percent.

4. A composition as defined in claim 1 wherein said polymer is obtained by copolymerizing from 1 to 5 molar percent of maleic anhydride with from 20 to 30 molar percent of a C to C fatty alcohol ester of a butenedioic acid and from to molar percent of a vinyl ester of a short chain C to C fatty acid.

References Cited by the Examiner UNITED STATES PATENTS 2,892,690 6/1959 Lowe et al. 4462 2,914,479 11/1959 Torn et al. 44 5s 2,927,013 3/1960 Lowe et a1. 44--62 2,995,928 10/1960 Smith etal 4456 FOREIGN PATENTS 808,737 1/1959 Great Britain.

DANIEL E. -WY MAN, Primary Examiner. 

1. AN IMPROVED MOTOR GASOLINE CHARACTERIZED BY A REDUCED TENDENCY TO FORM OBJECTIONABLE ENGINE DEPOSITS, SAID GASOLINE CONTAINING SOLVENT OIL HAVING VISCOSITY OF BETWEEN 50 AND 2000 SUS AT 100*F. IN A MINOR AMOUNT SUFFICIENT TO IMPROVE UPPER CYLINDER LUBRICATION AND A VERY SMALL AMOUNT OF A POLYMRIC ADDITIVE SUFFICIENT TO IMPART OXIDATION STABIITY TO SAID SOLVENT OIL AND TO PROMOTE ENGINE CLEANLINESS, WHICH PLYMER IS OBTAINED BY COPOLYMERIZING FROM 1 TO 6 MOLAR PERCENT OF MALEIC ANHYDRIDE WITH FROM 20 TO 50 MOLAR PERCENT OF A C8 TO C20 FATTY ALCOHOL ESTER OF AN A,B-UNSATURATED C4 TO C6 DICARBOXYLIC ACID AND WITH FROM 40 TO 80 MOLARPERCENT OF A COPOLYMERIZABLE ALKENYL C2 TO C6 ESTER OF AN ALIPHATIC MONOCARBOXYLIC ACID TO GIVE A POLYMER HAVING A MOLECULAR WEIGHT OF FROM 100,000 TO 3,000,000. 